In Flash memory devices with the MirrorBit™ architecture, developed by Advanced Micro Devices™, two bits are stored per cell, with each bit independent of the other. FIGS. 1A and 1B illustrate a surface view and a cross sectional view, respectively, of a chip during the testing of a plurality of these multiple independent bit Flash memory devices. During in-line processing, the chip 100 comprises a plurality of polysilicon lines 102.1-102.5 on a substrate 108. Between the polysilicon lines 102.1-102.5 are oxide lines 104.1-104.4. Bridge defects 106 can occur during manufacturing of polysilicon lines 102.1 and 102.2, which would short the devices containing them.
For Flash memory devices, some bridge defects can be detected using an optical inspection tool. However, an optical inspection tool is limited by the grain/surface noise and may not have the resolution required to detect the bridging in multiple independent bit Flash memory devices. A Scanning Electron Microscope (SEM) tool can be used to view material differences between the polysilicon lines 102.1-102.5 and the oxide lines 104.1-104.4 in conventional Flash memory devices. The bridge 106 would have the same shade as the polysilicon lines 102.1 and 102.2 and a different shade as the oxide line 104.1. However, with multiple independent bit Flash memory devices, the oxide lines 104.1-104.4 are very narrow, making the material contrast difference between the bridge 106 and the oxide line 104.1 very difficult to see.
Accordingly, there exists a need for an improved method for detecting bridge defects in multiple independent bit Flash memory devices. The present invention addresses such a need.